Artificial lung system and its methods of use

ABSTRACT

An oxygen supply unit for use with a blood oxygenator comprises an oxygen concentrator and a carbon dioxide scrubber. In an on-line operational mode, oxygen-rich gas from the oxygen concentrator is predominantly supplied to the blood oxygenator with a reduced flow of recycled gas from the concentrator. In an off-line operational mode where the oxygen supply unit is being powered by battery only, a larger flow of recycled gas from the blood oxygenator is passed through the carbon dioxide scrubber and combined with a lesser amount of oxygen-rich gas from the oxygen concentrator. The oxygen supply unit may be used in combination with a blood pump and oxygenator to provide ambulatory blood oxygenation to patients with compromised lung function.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International PCT Application No.PCT/US2015/061214, filed in the United States Patent & Trademark Officeas the Receiving Office on Nov. 18, 2015, which application claims thebenefit of U.S. Provisional Application No. 62/081,747, filed Nov. 19,2014, which applications are incorporated herein by reference.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under Grant numberHL118372 awarded by the National Institutes of Health. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

The present invention generally relates to systems and methods foroxygenating blood. More specifically, the invention relates to systemsand methods for oxygenating blood in an ambulating patient.

BACKGROUND

Lung failure occurs acutely or chronically. Lung disease is the numberthree killer in the United States and is responsible for one in sixdeaths. Chronic obstructive pulmonary disease (COPD) is one of the mostcommon lung diseases and is the fourth leading cause of death in theU.S. Adult Respiratory Distress Syndrome (ARDS) is afflicting 190,000patients yearly and the average survival is between 30-50% (Rubenfeld etal. N Engl J Med 2005;353:1685-93). If lung failure occurs, eithermechanical ventilation or extracorporeal membrane oxygenation (ECMO)must be implemented to oxygenate the blood to maintain the oxygenrequirements of the body. Mechanical ventilation is effective forshort-term support, yet the sustained tidal volumes and airway pressuresoften used may damage the lungs.

ECMO systems are an attractive alternative to mechanical ventilationsince they closely simulate physiological gas exchange and extended ECMOsupport is possible via multiple device exchanges. But in practice,these systems are limited by the complexity of their operation,bleeding, and reduced patient mobility. The patients are oftenbedridden, resulting in muscular atrophy.

Recently, ambulatory ECMO support has been implemented in a number ofcenters using available pumps and oxygenators, allowing patients to walkaround and go outside. They can also eat and exercise. In spite of thebenefits that current ECMO systems provide, they are still very bulky.They are also limited for extended use due to the functional lifespan ofoxygenators. In consideration of the limitations described above, thereis a need in the art for a system and method for providing mechanicaloxygenation for an ambulating patient using a portable artificial lungsystem that is suited for extended use.

Patents and published applications relevant to the subject natter of thepresent invention include US2013296633; US2011040241; U.S. Pat. No.7,682,327; U.S. Pat. No. 6,935,344; U.S. Pat. No. 6,503,450; U.S. Pat.No. 5,308,320; U.S. Pat. No. 4,548,597; U.S. Pat. No. 4,610,656; andU.S. Pat. No. 3,927,981.

SUMMARY OF THE INVENTION

Techniques are provided for mechanical oxygenation of an ambulatingpatient using an artificial lung system that provides one or moreadvantages over the previously available oxygenation systems. While thesystems of the present invention are particularly suitable as portablesystems, they may also be used as or as part of stationary systems.

In a first set of embodiments, a blood oxygenation system includes amulti-lumen cannula that communicates with a pump oxygenator unit and asupply pack that provides a power source and an oxygen source. The pumpoxygenator unit is configured to be disposable and removable from therest of the system.

In one aspect of the invention, the pump oxygenator unit is configuredto continuously oxygenate blood for more than thirty days without havingto be replaced.

In another aspect of the invention, the blood is removed from thepatient and returned to the patient through a dual lumen catheter whichcomprises a first lumen for removing non-oxygenated blood and a secondlumen for returning oxygenated blood to the patient's circulatorysystem. The catheter may further comprise a self-sealing mechanism toallow for the cannula to be inserted directly into the right ventricleof the heart.

In yet another aspect of the invention, the supply pack is a portableunit that can include wheels to allow the patient to pull the unit.

In another variation, the supply pack has one or more straps to allowthe patient to wear the pack as a backpack or satchel.

In another variation, the oxygen source may be an oxygen generator, anoxygen tank, or a combination of both.

In a second set of embodiments, a method of providing mechanicalventilation to an ambulating patient is provided which includes removingnon-oxygenated blood from the circulatory system of a patient, passingthe blood through a pump and oxygenator located on the body, andreturning the newly oxygenated blood back to the circulatory system ofthe patient; wherein the pump communicates with a pump motor andcontroller that are separately housed in a portable pack; and whereinthe oxygenator is supplied with oxygen from a portable source that isseparately housed. The method optionally includes the use of a portablepack to house the pump motor, controller, and oxygen source.Alternatively, as illustrated hereinafter, the pump and/or theoxygenator may be carried on a belt worn around the patient's waist.

In another aspect, the present invention provides a compact, low-weightoxygen supply unit for a lung-assist oxygenator system that can deliveran oxygen flow rate typically in the range 0.5 to 3 liter per minuteusing a pressure-swing type oxygen concentrator in combination with adisposable carbon dioxide scrubber unit. The oxygen supply unit can runusing battery power (“off-line” operation) or using AC or plug-incurrent (“on-line” operation). Use of the carbon dioxide scrubberincreases battery life since the scrubber requires less power to recycleoxygen than does the oxygenation concentrator to produce oxygen. Notusing the carbon dioxide scrubber while the system is powered from anexternal source, however, is preferable since the power source isunlimited and the life of the carbon dioxide scrubber can be extended(the scrubbing medium is not being consumed), allowing use of a smallerscrubber and/or less frequent scrubber exchange. In this way, the sizeand weight of the oxygen supply unit can be minimized and the batteryoperation time maximized.

During off-line or battery operation, oxygen-rich gas from the oxygensupply unit enters the blood oxygenator where it exchanges oxygen forcarbon dioxide and produces an exhaust gas having an increased carbondioxide content. The amount of carbon dioxide, however, is not great.Rather than dumping this exhaust gas which still contains a high levelof oxygen into the environment, the gas can be returned to the oxygensupply unit where it is scrubbed to remove the carbon dioxide, typicallyafter removing water vapor. The scrubbed gas is recycled back to theblood oxygenator unit with the addition of a small flow of concentratedoxygen from the oxygen concentrator unit sufficient to replace theamount of oxygen which was transferred during the previous passagethrough the blood oxygenator. In this way, a high oxygen rich gas flowrate, on the order of 5 to 10 liters per minute, can be provided to theoxygenator using only 0.5 to 1 liters per minute of oxygen from theoxygen concentrator to reduce power consumption and extend battery life.

When the patient is able to plug in the oxygen supply unit (“on-line”operation), power consumption is no longer a concern and output of theoxygen concentrator is increased, allowing flow though the carbondioxide scrubber to be bypassed. Consumption of scrubbing medium is thusprevented during on-line operation, so the size or the scrubber can bereduced and/or the usable life of the scrubber can be extended,minimizing the replacement frequency. The size of the oxygen supply unitcan be further minimized by using a relatively low output 0.5-3 literper minute oxygen concentrator in combination with the disposable carbondioxide scrubber canister, making the dual operation mode oxygen supplyunit of the present invention cheaper, smaller, and lighter in totalsize and weight than an equivalent battery-only system where the carbondioxide scrubber must be sized to accommodate constant operation.

In accordance with a particular method of the present invention, anoxygen-rich gas stream useful for blood oxygenation may be produced byselectively operating an oxygen concentrator from either battery poweror an external power source, typically line power from the grid or froma local generator. Oxygen from the oxygen concentrator will be deliveredwithout scrubbing to a blood oxygenator when the oxygen concentrator isoperating from the external power source. In contrast, oxygen from theoxygen concentrator will be combined with a carbon dioxide-scrubbedoxygen gas stream, and the combined gas stream delivered to the bloodoxygenator, when the oxygen concentrator is operating from the battery.In this way, battery life can be increased while simultaneouslyextending the life of and/or reducing the size of the carbon dioxidescrubber which is utilized.

In some embodiments, the carbon dioxide-scrubbed gas stream is producedby scrubbing carbon dioxide from a carbon dioxide elevated gas streamreceived from the blood oxygenator. Usually, the oxygen concentratordelivers a flow in the range from about 0.5 liters per minute (LPM) to 1LPM to combine with the carbon dioxide-scrubbed gas stream. Usually, thecarbon dioxide-scrubbed gas flow is in the range from 4.5 LPM to 9 LPM.

In embodiments where oxygen from the oxygen concentrator is delivered tothe blood oxygenator without scrubbing, the oxygen is delivered at arate in the range from 2 LPM to 6 LPM. In such instances, the oxygenfrom the oxygen concentrator may be further combined with a carbondioxide-elevated gas stream from the blood oxygenator. In theseinstances, as a higher oxygen flow rate is provided by the oxygenconcentrator, there is no need to scrub the carbon-dioxide elevated gasstream as is the case during off-line operation. The carbon dioxideelevated gas stream will usually be combined with the oxygen from theoxygen concentrator at a rate from 3 LPM to 6 LPM.

In accordance with a particular apparatus of the present invention, anoxygen supply unit intended for use with a blood oxygenator comprises anoxygen concentrator, a carbon dioxide scrubber, a power control, and avalved tubing network. The oxygen concentrator is configured to producea concentrated oxygen stream from air, typically comprising apressure-swing oxygen concentrator driven by an internal electricalcompressor. The carbon dioxide scrubber is configured to receive a“recycled” stream of elevated carbon dioxide gas flow from the bloodoxygenator and to remove or “scrub” carbon dioxide from that stream,typically removing substantially all carbon dioxide. As the recycledelevated carbon dioxide gas flow from the blood oxygenator will stillcomprise well over 90% of the oxygen originally present, once the carbondioxide is removed, it is suitable for return to the blood oxygenatorafter it is combined with an amount of oxygen from the oxygenconcentrator which is sufficient to replace that which has been removedduring the previous pass of the gas stream through the blood oxygenator.The power control is configured to selectively deliver power from eithera battery source or an external power supply, typically an AC wall plugavailable in most places. The valve tubing network is configured todeliver oxygen-rich gas from the oxygen concentrator to the bloodoxygenator without scrubbing when the power control delivers power fromthe external power supply to the oxygen supply unit. The valve tubingnetwork is further configured to combine oxygen-rich gas from the oxygenconcentrator with the carbon dioxide-scrubbed gas being recycled fromthe carbon dioxide scrubber when the power control delivers power fromthe battery. Such dual-mode operation has the advantages of powerefficiency and reduced scrubbing medium consumption as described abovein connection with the methods of the present invention.

The oxygen supply units of the present invention will typically beenclosed within a shell or an enclosure, and the shell or enclosuretypically comprises wheels configured to allow the enclosure to bepulled or pushed by a user. Alternatively, the enclosure could beconfigured to be worn as a backpack (optionally by an individual otherthan the patient), mounted on a wheel chair, mounted in a car, airplane,or other vehicle, or the like. Still further alternatively, theenclosure could be configured for stationary placement.

The carbon dioxide scrubber may be a conventional canister-type scrubberhaving a commercially available scrubbing medium, such as a soda lime,suitable media being commercially available under the trade namesLitholyme®, Sodasorb®, Medisorb®, Sodasorb® LF, and Amsorb®.

The valved tubing networks of the oxygen supply units of the presentinvention will typically further comprise a dehumidifier for removingmoisture from the elevated carbon dioxide gas flow prior to that gasflow passing through the carbon dioxide scrubber. Useful dehumidifiersinclude commercially available Nafion® gas driers. The valved tubingnetworks will usually further comprise a pump for flowing the elevatedcarbon dioxide gas stream through the carbon dioxide scrubber andcombining the gas stream with the oxygen stream from the concentratorwhich is at a relatively higher pressure. Other features of the valvedtubing network include a bypass line which allows the oxygen-rich gas toflow by the carbon dioxide scrubber during online operation. Still otherfeatures include disconnects which allow the carbon dioxide scrubbingcanister to be removed and replaced from the oxygen supply unit withminimal difficulty.

The oxygen supply units of the present invention, as described above,may be combined with a pump-blood oxygenator unit configured to be wornby a patient. The blood pump oxygenator units typically include ablood-oxygenator having a semi-permeable membrane matrix allowingoxygen-carbon dioxide exchange as blood and the oxygen-rich air streamflow through the oxygenator. These systems will typically furthercomprise an umbilical cord or cable for connecting the oxygen supplyunit to the blood-pump oxygenator. The umbilical cord will include tubesfor delivering the oxygen-rich gas from the oxygen supply unit to thepump-blood oxygenator as well as for returning elevated carbon dioxidegas from the blood pump oxygenator to the oxygen supply unit. Theumbilical cables will still further include electrical lines fordelivering power and/or control signals from the oxygen supply unit tothe blood-pump oxygenator.

Still other aspects, features and advantages of the invention arereadily apparent from the following detailed description, simply byillustrating a number of particular embodiments and implementations,including the best mode contemplated for carrying out the invention. Theinvention is also capable of other and different embodiments, and itsseveral details can be modified in various obvious respects, all withoutdeparting from the spirit and scope of the invention. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized. The presentinvention is illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings, in which likereference numerals refer to similar elements, and in which:

FIG. 1 illustrates one example configuration of an ambulatory blood pumpoxygenation system including an oxygen supply unit and a pump oxygenatorcombination;

FIG. 2 depicts one example configuration of the cannula that introducesoxygenated blood and removes non-oxygenated blood from the circulatorysystem;

FIG. 3 illustrates one example configuration of the pump oxygenatorunit;

FIG. 4A illustrates an alternate embodiment of an ambulatory oxygensupply unit of the present invention including an oxygen concentrator inplace of an oxygen tank.

FIG. 4B illustrates a pump oxygenator unit secured to a patient's waiston a belt showing an umbilical suitable for connecting to an ambulatoryoxygen supply unit;

FIGS. 5A and 5B illustrate operation of the oxygen supply unit of FIG. 4including selective carbon dioxide scrubbing and battery/plug-inoperation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method and system are described for the long term mechanicaloxygenation of an ambulating patient. In the following description, forthe purpose of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without these specific details. In otherinstances, well-known structures and devices are shown in block diagramform in order to avoid unnecessarily obscuring the present invention.

The system of the present invention provides a long-term solution toenable a person in need of blood oxygenation, the ability to no longerbe bed ridden. The system comprises a pump oxygenator unit thatinterfaces with the patient's circulatory system via a multi-lumencannula. The pump oxygenator unit is capable of oxygenating blood for anextended period of time. A portable supply pack provides the necessarypower and oxygen source to the system.

Referring now to the figures, FIG. 1 depicts one embodiment of theportable blood oxygenator system, 100. System 100 comprises amulti-lumen cannula 120, blood oxygenator 310, blood pump 320, and aportable supply pack 130. One example embodiment of the multi-lumencannula 120 is further depicted in FIG. 2. In this example, cannula 120comprises an elongated body 210 having a drainage cannula and a returncannula. Drainage cannula 220 and return cannula 230 have inner lumens,both of which run the length of the elongated body. Drainage cannula 220has a proximal end 222 and a distal end 224. Return cannula 230 also hasa proximal end 232 and a distal end 234. The proximal ends of thedrainage and return cannulas are configured to communicate with pumpoxygenator combination 310/320. The connections between the ends of thecannulas and the pump oxygenator unit are detachable. Drainage cannula220 is configured to receive non- oxygenated blood from the rightventricle of the heart and send it back to the pump oxygenator unit. Thereturn cannula is configured to return oxygenated blood into thepulmonary artery from the pump oxygenator unit. Cannula 120 furthercomprises a self-sealing mechanism 240 near the distal end to preventblood leakage from the heart where the cannula is inserted. In certainembodiments, self-sealing mechanism 240 is detachable from the elongatedbody.

FIG. 3 depicts one example configuration of a pump oxygenator unit. Theunit comprises a blood oxygenator 310 and blood pump 320. The bloodoxygenator may be any blood oxygenator known in the art. However, incertain embodiments, a blood oxygenator that provides uniform blood flowand oxygen diffusion is preferred. In the illustrated embodiment, bloodpump 320 includes an inlet 322 that is configured to receivenon-oxygenated blood from drainage cannula 220. The non-oxygenated bloodtravels from the blood pump and into the oxygenator through oxygenatorinlet 312. Oxygen which is received from the oxygen source at gas inlet314 is diffused into the blood as it travels through the oxygenator.Once oxygenated, the blood travels through outlet 316 which communicateswith return cannula 230. Exhaust gas is released through outlet 318. Theblood pump communicates with the electric motor drive located in thesupply pack as described below. This connection is detachable at thepump in certain embodiments.

Supply pack 130 houses a power source 132, an electric motor drive 136and one or more oxygen sources 138. The supply pack is configured to bea portable system that can readily be moved and transported by the user.In certain embodiments, the supply pack housing includes wheels and ahandle to allow the user to pull the unit. However, the supply pack mayalso be housed in a wearable case such as a backpack, satchel, or wastepouch. Power source 132 is configured for long-term, portable use. Anytype of battery may be used to power the system including bothrechargeable and non-rechargeable options.

Oxygen may be supplied to the patient by oxygen generator 134 or anoxygen source 138. In certain embodiments, the supply pack includes anoxygen generator as well as an oxygen source that may be used as areserve. Oxygen source 138 is generally a compressed gas tank thatincludes a regulator at the outlet to control the volume and rate ofoxygen that is released into the system. A series of oxygen tanks may beused in certain embodiments. The size and number of oxygen sources, ortanks that are housed in the supply pack will depend on the user'sneeds. Electric motor drive 136 is powered by power source 132 andoperates pump oxygenator unit 110. A controller communicates with pump320 via a cable that runs from the supply pack to the pump. Thecontroller is responsible for varying the motor speed to maintain theoxygen needs of the user.

Blood oxygenators must be replaced periodically due to thrombosis thatoccurs on the membranes that allow for gas transfer. In certainembodiments, the pump oxygenator unit is separate from the electricmotor drive to allow for the replacement of the pump oxygenator unitwithout having to replace the more costly electric motor drive. The pumpoxygenator unit is capable of continued use for thirty days or more.When replacing the pump oxygenator unit, the cannula is removed frominlet 322 and outlet 316. The electric motor drive is also detached fromthe pump and the oxygen source is detached at 314. In other embodiments,the oxygenator is the only element of the system that must be replacedon a regular basis.

Another aspect of the present invention provides a method of providingpermanent mechanical oxygenation to an ambulating patient in need. Themethod includes (a) directing non-oxygenated blood from the circulatorysystem of a patient through an inlet in a pump and an oxygenator; and(b) returning the oxygenated blood to the circulatory system of saidpatient; wherein the pump and oxygenator are part of a portable systemwhich comprises a portable power source and oxygen source housed in apack. In one variation of the method, the blood oxygenator is capable ofcontinuously oxygenating blood for more than thirty days.

Referring now to FIG. 4A, an alternative embodiment of an oxygen supplyunit constructed in accordance with the principles of the presentinvention comprises a frame 402 which is typically mounted on wheels 404to allow mobility and easy repositioning. A shell or enclosure 406 istypically provided in order to enclose a plurality of system components,including an oxygen concentrator 408, a battery 410, a carbon dioxidescrubber 412, a recirculating pump 414, a dehumidifier 416, and acontrol unit 418. The oxygen concentrator may be a commercial unitselected to provide a concentrated oxygen flow in the desired flowrange, typically from 1 LPM to 3.5 LPM. Typically, the oxygenconcentrator will employ the pressure-swing principle which divides theair into a high oxygen concentration stream and a high nitrogenconcentration stream. The high oxygen concentration stream will be usedand the nitrogen stream released back to the atmosphere. The battery maybe any conventional rechargeable battery, typically being a lithium ionbattery or the like. The carbon dioxide scrubber will typically comprisea canister filled with a soda lime or other scrubbing medium, as hasbeen previously described herein. The recirculation pump will be used inorder to deliver elevated carbon dioxide gas from the blood oxygenatorto the scrubber, as will be described in more detail below. Thedehumidifier is typically a coil which condenses out water from therecycled elevated carbon dioxide stream from the blood oxygenator, e.g.,a Nafion® gas dryer. In some embodiments, the dryer 416 is located abovethe oxygen concentrator 408, as shown in full line. In otherembodiments, the dryer 416 a is located below the oxygen concentrator,as shown in broken line, thus exposing the dryer tubes directly to hotgas produced by the concentrator. The latter design is an advantage asit avoids ducting which is necessary if the dryer is above theconcentrator, allowing a more compact design. The control unit willtypically provide an operator interface and also include controlcircuitry and logic which manages the valving system and powerdistribution system as described in more detail below with respect toFIGS. 5A and 5B. The umbilical cord 420 provides for convenientattachment to the pump-blood oxygenator unit (or pump oxygenator unit)440 (FIG. 4B) which is worn by the patient. The umbilical cord includesan oxygen-rich gas line 422, an elevated carbon dioxide gas line 424,and one or a plurality of power/control line(s) 426. In addition, aplug-in power line 428 will be provided for use when it is possible toplug the unit into an AC or other external power source. Referring nowto FIG. 4B, a pump oxygenator unit 440 may be worn by the patient P, forexample on a belt at the patient's waist. The pump oxygenator unit 440will include a blood oxygenator 442 and a blood pump 444. The pump 444receives venous blood from the patient and delivers the venous bloodinto the blood oxygenator 442. Oxygenated blood from the oxygenator 442returns back to the patient on the arterial side of the vasculature. Forexample, a cannula 450 may be used for delivering blood to and from thepatient, as described in copending application PCT/US2015/060127, for“Self-Sealing Cannula,” filed on Nov. 13, 2015, the full disclosure ofwhich is incorporated herein by reference.

Referring now to FIG. 5A, the layout of the components of the oxygensupply unit 400 will be described in more detail. The oxygenconcentrator 408 is mounted within the enclosure 406 and connected tothe ambient to receive an inflow of air. Power is delivered to theoxygen concentrator 408 from a power control unit 418, and may be eitherpower from the battery 410 or from the line cord 428. As shown in FIG.5A, the power is coming from the battery 410 as the line cord 428 is notconnected. The power control may be configured to automatically detectthe power source based on whether or not the line cord 428 is connectedto an AC current source. When the oxygen supply unit 400 is notconnected to the AC power source, elevated carbon dioxide gas enteringthrough line 424 passes through the dehumidifier 416 and is pumped byrecirculating pump 414 through a control valve 500 which directs theelevated carbon dioxide gas to the carbon dioxide scrubber 412 through asecond valve 502 and a quick disconnection fitting 504. A ventedT-fitting 503 is optionally provided to exhaust excess elevated carbondioxide gas from the system to the ambient. The vented elevated carbondioxide gas volume will be equal to the net inflow volume from theoxygen concentrator 408. Other excess gas exhaust mechanisms might alsobe used. Often, there will be liquids in carbon dioxide gas line 424exiting the oxygenator unit 442, including condensed water vapor and asmall amount of blood plasma. A separator (not shown) will typically beprovided as part of the oxygen supply unit 400 or alternatively in thesupply line 424 to remove these liquids.

The elevated carbon dioxide gas from pump 414 combines with oxygen fromthe oxygen concentrator 408 through a T-junction 506. As describedpreviously, from 4.5 LPM to 6 LPM of the elevated carbon dioxide gaswill typically pass through the carbon dioxide scrubber with theaddition of approximately 1 LPM of oxygen-rich gas from the oxygenconcentrator 408. The relative amounts delivered can be controlled viathe pump 414. Scrubbed oxygen-rich gas from the carbon dioxide scrubber412 passes out through a quick disconnect 508 and further control valve510 which allows the gas to pass into the oxygen-rich gas line 422 backto the blood oxygenator 442. Gas flow may continue in this pattern forso long as the blood supply unit 400 remains disconnected from AC power.In this efficient operational mode, the battery life will typically lastat least several hours, and may last as many as 4 hours, 5 hours, 6hours, or longer.

Once the patient reaches a location where AC or other external power isavailable, the user may plug the power line into an AC power source, asshown in FIG. 5B. Once line current is available, operation of theoxygen supply unit 400 may be changed in order to preserve the carbondioxide scrubbing media to extend the life of the scrubber and/or reducethe size of the scrubber. In particular, oxygen from the oxygenconcentrator will now bypass the carbon dioxide scrubber through abypass line 520 which was previously isolated by valves 500 and 510.Valves 500 and 510 are now reconfigured to allow passage of theoxygen-rich gas through the bypass line 520. Similarly, valves 502 and510 are arranged to block flow through the CO₂ scrubber. While in thisconfiguration, the carbon dioxide scrubber 412 may be removed andreplaced using the quick disconnect elements 504 and 508. During onlineoperation, the volume of oxygen-rich gas from the oxygen concentratorwill be increased, typically to the range from 2.5 LPM to 3.5 LPM.Elevated carbon dioxide gas entering through line 424, however, willcontinue to be recycled and mixed with the oxygen- rich gas, although ata lower flow rate, typically in the range from 3 LPM to 6 LPM. Mixingoccurs in valve 500 and the relative flow volumes can again becontrolled using pump 414. The combined rich oxygen gas stream andelevated carbon dioxide gas stream flow through the bypass line 520 andout through valve 510 where they can enter oxygen-rich gas line 422 andreturn to the blood oxygenator 442.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. A method for providing oxygen rich gas for bloodoxygenation, said method comprising: selectively operating an oxygenconcentrator from battery power or from an external power source;delivering oxygen from the oxygen concentrator without scrubbing to ablood oxygenator when the oxygen concentrator is operating from theexternal power source; and combining oxygen from the oxygen concentratorwith a carbon dioxide-scrubbed oxygen gas stream and delivering thecombined gas stream to the blood oxygenator when the oxygen concentratoris operating from the battery.
 2. A method as in claim 1, furthercomprising producing the carbon dioxide-scrubbed gas stream by scrubbingcarbon dioxide from a carbon dioxide elevated gas stream received fromthe blood oxygenator.
 3. A method as in claim 2, wherein the oxygenconcentrator delivers a flow in the range from 0.5 LPM to 1 LPM tocombine with the carbon dioxide-scrubbed gas stream.
 4. A method as inclaim 3, wherein the carbon dioxide-scrubbed gas flow is from 4.5 to 9LPM.
 5. A method as in claim 1, wherein oxygen from the oxygenconcentrator without scrubbing is delivered at a rate from 2 LPM to 6LPM.
 6. A method as in claim 5, further comprising combining the oxygenfrom the oxygen concentrator with a carbon dioxide elevated gas streamfrom the blood oxygenator.
 7. A method as in claim 6, wherein the carbondioxide elevated gas stream flows at a rate from 3 LPM to 6 LPM.
 8. Anoxygen supply unit for a blood oxygenator which receives an oxygen richgas flow and generates an elevated carbon dioxide gas flow, said oxygensupply unit comprising: an oxygen concentrator which produces an oxygenrich gas stream from air; a carbon dioxide scrubber which removes carbondioxide from an elevated carbon dioxide gas flow; a power control whichselectively delivers power from a battery or an external power supply;and a valved tubing network configured (1) to deliver oxygen rich gasfrom the oxygen concentrator to the blood oxygenator without scrubbingwhen the power control delivers power from the external power supply and(2) to combine oxygen rich gas from the oxygen concentrator with carbondioxide-scrubbed gas from the carbon dioxide scrubber when the powercontrol delivers power from the battery.
 9. An oxygen supply unit as inclaim 8, further comprising an enclosure wherein the oxygenconcentrator, the carbon dioxide scrubber, the power control, and thevalved tubing network are disposed within the enclosure.
 10. An oxygensupply unit as in claim 9, wherein the enclosure comprises wheelsconfigured to allow the enclosure to be pulled or pushed by a user. 11.An oxygen supply unit as in claim 8, wherein the oxygen concentratorcomprises a pressure-swing oxygen concentrator having an electronicallydriven internal compressor.
 12. An oxygen supply unit as in claim 8,wherein the carbon dioxide scrubber includes a canister having ascrubbing medium.
 13. An oxygen supply unit as in claim 12, wherein thescrubbing medium comprises soda lime, Litholyme®, Sodasorb®, Medisorb®,Sodasorb® LF, and Amsorb®.
 14. An oxygen supply unit as in claim 8,wherein the valved tubing network comprises a dehumidifier for removingmoisture from the elevated carbon dioxide gas flow prior to passing saidflow through the carbon dioxide scrubber.
 15. An oxygen supply unit asin claim 14, wherein the valved tubing network further comprises a pumpfor flowing the elevated carbon dioxide gas stream.
 16. An oxygen supplyunit as in claim 15, wherein the valved tubing network further comprisesa bypass line which allows the oxygen rich gas to flow by the carbondioxide scrubber.
 17. A system comprising: an oxygen supply unit as inclaim 8; and a pump-blood oxygenator unit configured to be worn by apatient.
 18. A system as in claim 17, further comprising an umbilicalcable including an oxygen rich flow tube, an elevated carbon dioxideflow tube, and an electrical line which connects a pump of thepump-blood oxygenator unit to the power control of the oxygen supplyunit.